Metallic blasting and abrasive material



' nation of properties.

Patented N ov. 7.,

PATENT. OFFICE 2.362.310 Momma nms'rmo AND anaaslvn MATERIAL Franklin-B. Itote, Ann Arbor, Mi h,- assignor to The International Nickel Compan y, Inc., New

York, Y., a corporation Delaware No Drawing. Application December 29, 1942, I Serial No. 470,517 a .6 Claims. (0]. 51-409) The present invention relates to metallic blasting and abrasive material used in processes where the blasting "material is thrown at. highvelocities against an object by air or other gas pressure or by mechanical force to'clean the-object 6 .or to obtain an abrading effect, and more per.

ticuiarly to cast iron shot and the like to be used in its cast or spherical form in such processes. It has been proposed to make shot and the like to be used directly, i. e., not crushed and used as 10 grit, of. hard white cast iron or of soi't male leabilized cast iron, but such blasting andabrasive material was not completely satisfactory in actual commercial practice. Unalloyed white iron shot possessed high hardness, but lacked the desired toughness and shattered onimpact. Some modified compositions exhibited moderate, improvement in toughness, but shot having such compositions still suffered trim the disadvantage 01' shattering upon impactwith the material being shot blasted and 01" having relatively short service life. Malleabilized cast .iron shot had a microstructure containing principally territe and temper carbon and possessed higher toughness than white iron shot, but its hardness and wear resistanoewas at a much lower level. Although many attempts .were made to remedy this and other shortcomings; none, as far as Lam aware, was entirely successful when carso ried into practice commercially.

I have discovered that an improved combinetion of properties, including high toughness, can

- be obtained by using a specialcomposition for metallic blastingand abrasivematerial to be arsed in its cast or substantially spherical form. 36

It is an object of the 'presentinvention to pro- I vide a chilled shot having an improved combi- It is another object of the invention provide a metallic blasting and abrasivem t ri ha 40 a e vmg impurities, including chromium, molybdenum,

a high degree or toughness at intermediate hardness levels.

It is a further object or the invention to provide a metallic blasting and abrasive material having increased service life. It is still another object or the invention to provide an improved austenltic carbidic alloy cast iron shot-which has adequate hardness combined wlth high toughness and decreased tendency'to high toughness o shatter in use. 1

It is? an object of the invention to provide a improvedcast ironshot having a simple composition. 1

Other objects and advantages of the invention to and may be desirable in certain instances.

will become apparent from the iollowing description. 1

. Generally speaking, the present invention provides an alloyed cast iron shot and the like to be used directly, 1. e., not crushed and used as grit, made of cast iron containing about 2% to 4% carbon,'about 0.2% to 1.5% manganese, about 0.5% to 6% nickel, and at least about 0.2% but less than 1.5% silicon. Manganese in amounts exceeding the amount required because ofits effect .on sulfur, which is usually about 0.2% to 0.5% manganese, promotes austenite formagitlain con contents within the range or about 0.5% to 1.2% have given satisfactory results. In addition to the foregoing elements, the cast iron of.

the present invention may contain up to about 2% chromium, e. g., about 0.1% to 1.5% chromium, but' the presence of chromium is not es-- sential to obtain the improved combination of properties, particularly-toughness and hardness, which "characterizes the cast iron shot provided byathe present inven on. Chromium, e. g., about 0.25%, maybe bene cial, particularly when the nickel is less than about 2%, inhpromoting austenite formation. In actual practice, it is preferred to maintain the nickel within-'the-range or about 3.5%to 5% and to maintain the silicon within the range of about 0.5% to 1%. The shot of the present invention may also contain small amounts of incidental or minor constituents and impurities added for known purposes or present as the resultof commercial practice, e. g., sul-. fur, phosphorus, titanium, etc. Qlhus, the cast iron shot-may, contain about. 0.02% to 0.2%01' sulfur, about 0.03% to 1% or phosphorus, about 0.01% to 0.05% of titanium, etc. It is to be un-- derstood that when the term balancesubstantially all-iron? is used herein, it is not desired to exclude incidental or minor constituentsgrsulfur. phosphorus, etc. which may be present in such amounts as occur in commercial products or in amounts not adversely affecting the desired propertiespf the cast iron shot.

It is a critical feature or the improved shot that a balanced composition be maintained within the ranges set "forth hereinbeiore. If the sili. con content excee theamounts set forth, the

e shot, provided by the invention is no longer obtained. Thus, a cast iron shot containing about 3.23% total carbon, about 1.53% silicon, about 0.36% manganese, and about 2.34% nickel had a Vickers' hardness number 0L about 831 to 804 and an impact value of about ,as in ordinary cast iron castings.

2.9 to 3.5 inch pounds measured as set forth hereinafter by a drop test, and was harder and muchless tough than the shot provided by the present invention. It has been found that the effect of silicon in cast iron'shot is not the same Low silicon contents in shot apparently'promote increased toughness and. decreased hardness and favor austenite formation, whereas in ordinary castings low silicon contents promote high hardness and brittleness and favor chill formation. Nickel in the amounts set forth hereinbefore is also essen. tial to obtain the desired high toughness combined with satisfactory hardness to give good wear resistance and service life.

The improved cast iron shot provided by the I invention contains a large proportion of austenite and has a microstructure constituted substantially entirely of carbide, i. e., cementite, and austenite. Martensite or other austenite decomposition products areusually absent and should not be present in more than small amounts, e. g., about of the matrix. The grain size of the cast iron in the shot is markedly decreased compared to othe cast iron shot. The carbide net work is markedly refined to produce a cell structure apparently of finely divided carbides surrounded .by austenite rather than a structure containing the more massive carbides usually found in plain unalloyed cast iron shot.

Ingrder that those skilled in the art may have a bet er understanding of the present invention, illustrative examples are given "in the following table of the carbon, silicon and nickel contents of cast iron shot produced in accordance with the present invention. The Vickers hardness number and the relative impact strength in inch ness. For example, a plain unalloyed iron containing 2.9% .total carbon and 1.0% silicon had a Vickers hardness of 461. With a nickel condecrease in hardness of the much tougher nickelcontaining shot over that of unalloyed cast iron shot apparently does not have a detrimental effet. Comparison of the shot oi. the present in--v vention with a commercial malleabilized shot showed that the toughness of the higher nickel content shot was substantially the same'as that of the malleabilized shot, but all the shot made in accordance with the invention had much higher hardness. For example, a malleabilized shot had an average Vickers hardness of 162 and an impact strength of 7.4 inch pounds as compared to a much higher Vickers hardness of 434 in combination with a similar impact strength of 7.4 inch pounds for shot No. 5 set forth in the table. 4

The present invention is fapplicable to the production of metallic blasting and abrasive material, particularly to the production of tough shot which is to be used directly in its cast substantially spherical form, 1. e., not crushed and used as grit, and where shattering is undesirable. A brief description of some blast cleaning processes, apparatus, and illustrations of the differences in surfaces cleaned by shot and by grit may be found in Metals Handbook, 1939 Edition, pages 1142 and 1143. The use of shot blasting for purposes other than cleaning are also well known to those skilled in the art, e. g., for scale and metal removal, work hardening of steel, raising the fatigue life of springs and other parts subjected to vibratory stresses, cutting, polishing and grindpounds determined by single blow drop tests are 1 also set forth in the following table Impact values were obtained by dropping from a given height a weight of 0.6 pound that struck a shot specimen of about 0.075 inch diameter which was placed on a flat hard base. The weight was dropped from'various heights, each time onto a new-specimen, until one level was found fromwhich the weight would fracture the shot with a single blow.' If dropping the weight from one inch-lower failed to fracture the shot, the impact strength was taken as the product of the weight and the distanceit fell to.pro duce fracture. Similar tests on shot having a diameter of about 0.105 inch confirmed in general the tion, as those skilled in the art will readily understand. Such variations and modifications are considered to be within the purview and scope of theinvention and the appended claims.

I claim:

1. Metallic abrasive and blasting material made about. 2% to 4% carbon, 0.2% to 1.5% manganese, 0.2% to 1% silicon, 0.5% to 6% nickel and the balance substantially all iron. 2. Metallic abrasive and blasting material made of substantially spherical cast iron particles havhigh toughness indicated by the impact values set forth in the table which were obtained on shothaving a diameter of 0.0'15'inch. In some instances, for examplenin shot No. l and shot No. 4.

' creases progressively as the nickel content increases and this increased toughness is abcompaniedbya relatively slight decrease in the lharding a microstructure comprised substantially entirely of carbide and austenite, and containing 'about'2% to 4% carbon, 0.2% to 1.5% manganese, 0.2%to 1% silicon, 3.5% to 5% nickel and the balance substantially all iron.

3. As an article of manufacture, a cast iron particle of substantially spherical form and of .a size suitable-for shot blasting and the like made of cast iron havinga microstructure comprised substantially-entirely of carbide and austenite, and comprising about 2% to 4% carbon,

about 0.2% to 1.5% manganese, about 0.2% to 1.2% silicon, about 3.5% to 6% nickel, and the balance substantially all iron.

4. Asan article of manufacture, a cast iron particle of substantially spherical form and of 5. As an article of manufacture, castiron shot suitable for shot blasting made of cast iron having a microstructure comprised substantially en-' tirely of carbide andaustenite, and containing about 2%,to 4% carbon, about 0.2% to 1.5% 10 manganese, about 0.5% to 1.2% silicon, about 0.5% to 0% nickel and the balance substantially all iron. 1 i

6. Metallic cast iron chilled shot having a microstructure comprised substantially all of carbide and austenite, and containing about 2% to,

4% carbon, 0.2% to 1.5% manganese, 0.2% to 1.2% silicon, 0.5%1 6% nickel andthe balance substantially all iron. 

